write a test class for trigger?

Hi,

Can you please write a test class for this trigger, I don't know how to write the test class logic, Please help me out...

Trigger CreateorUpdateAsset on Contract_Product__c (before insert, before update) {

  //List for insert and update

List<Asset> insertASList = new List<Asset>();

List<Asset> updateASList = new List<Asset>();

// To map the newly created asset back to the contract products

Map<Id,Id> assetIDMap =new Map<Id,Id>();

for(integer i=0;i<trigger.new.size();i++){

Contract_Product__c cp= trigger.new[i];

//Check for the Product_Master__c.Is_Serviceable__c is checked from the formula field

if((Trigger.isInsert && Trigger.isBefore && cp.Product_Master_Is_Serviceable_Fr__c=='True') || (Trigger.isUpdate && Trigger.isBefore && cp.Product_Master_Is_Serviceable_Fr__c=='True'&& cp.Asset__c==null)){

//create a new record on Asset

Asset newAsset = new Asset();

newAsset.Name= cp.Product_Name__c;

newAsset.Quantity=cp.Quantity__c;

newAsset.Contract_Product__c=

newAsset.AccountId= cp.Account_Name__c;

insertAslist.add(newAsset);

}

//If it is an update - and if the old value is true - do nothing - else create AS

if(Trigger.isUpdate && Trigger.isBefore && cp.Product_Master_Is_Serviceable_Fr__c=='True'&& 

                              trigger.old[i].Product_Master_Is_Serviceable_Fr__c=='False'){

//create a new record on Asset

Asset newAsset = new Asset(id =cp.Asset__c);

newAsset.Name= cp.Product_Name__c;

newAsset.Quantity=cp.Quantity__c;

newAsset.Contract_Product__c=

newAsset.AccountId= cp.Account_Name__c;

updateASList.add(newAsset);

}

}

//Inserting the newly created asset

if(insertASList.size()>0) insert insertASList;

//Updating the existing asset information

if(updateASList.size()>0) update updateASList;

//Load into assetIDMap

for(Asset a: insertASList){

assetIDMap.put(a.Contract_Product__c, 

}

//go over the list of contract products and update the newly created asset values

for(integer i=0;i<trigger.new.size();i++){

Contract_Product__c cp= trigger.new[i];

if(assetIDMap.get(

cp.Asset__c=assetIDMap.get(

}

}

}